WO1999025031A1

WO1999025031A1 - Light emitting element having an optical element molded in a surface thereof

Info

Publication number: WO1999025031A1
Application number: PCT/US1998/023538
Authority: WO
Inventors: Jon Nisper; Vince Vancho
Original assignee: Donnelly Corporation
Priority date: 1997-11-06
Filing date: 1998-11-05
Publication date: 1999-05-20
Also published as: AU1307999A

Abstract

A light emitting device comprises a casing having a surface, at least one light emitting element for emitting light enclosed in the casing, and at least two wire leads, each wire lead having one end enclosed in the casing and electrically connected to the at least one light emitting element and an opposite end projecting from the casing. A molded diffractive optical element for focusing light emitted from the at least one light emitting element is formed on and integral with the surface of the casing.

Description

TITLE

LIGHT EMITTING ELEMENT HAVING AN OPTICAL ELEMENT MOLDED IN A SURFACE THEREOF

FIELD OF THE INVENTION

The present invention relates to a light emitting element having an optical structure molded into a surface thereof, and preferably to a light emitting diode (LED) having a molded surface which improves the optical properties of the LED.

BACKGROUND OF THE INVENTION

A conventional LED is made by encapsulating a semiconductor diode in resin. The diode is placed in the air space of a cavity so that two wire leads attached to the diode protrude from the cavity. Clear thermosetting resin is then poured or injected into the cavity to encapsulate the diode. When the resin hardens, it forms a hard, transparent surface over the diode. The completed assembly is sometimes referred to as a "jellybean" diode, because the overall rounded shape resembles a jellybean. For example, see Fig. l of U.S. Patent No. 4,780,752.

Figure 1 shows an example of a conventional jellybean diode (referred to herein as an LED) 100. As shown, LED 100 has a diode 10, two wire leads 20 and 25, and a transparent casing 30 encapsulating the diode and one end of each wire lead. When a voltage is applied across the free ends of the wire leads 20 and 25, the diode 10 emits radiation in a particular wavelength range, which depends on the material composition of the diode. As illustrated by the light rays 40 in Figure 1, the glowing light spreads out in all directions from the transparent casing 30. Thus, an LED made in the conventional manner has minimal light-directing properties.

Certain LED applications require that the light be directed in some way. To accomplish this, a separate lens may be provided to collect and shape light rays. As shown in Figure 1, a lens 50 may be placed in front of the diode 10. Lens 50 may collect and shape the light rays 40 into a light beam 60 which is directed toward a target 70. The lens 50 can be a refractive lens or a diftractive lens. The diftractive lens can be like a hologram or grating, either of which can have a single surface or plural surfaces which are flat or curved, either radially or asymmetrically. The lens 50 may also be a combination of a refractive lens and diftractive lens. Lens 50 may be located any distance from the jellybean diode 100, and can, in fact, be close enough to touch the jellybean diode. Several drawbacks are apparent from this arrangement. The need for a separate lens increases the number of components, requires alignment, and results in a greater cost and complexity. In addition, as is apparent from Figure 1, this arrangement is inefficient because many of the light rays 40 do not reach lens 50. Attempts have been made to overcome these problems. One approach is exemplified in U.S. Patent Nos. 4,698,730 and 4,143,394. This approach involves forming the surface of the LED casing in a shape that reflects light rays emitted toward the side of the casing in the direction of a target. For example, the casing may be a paraboloid, as shown in U.S. Patent No. 4,698,730, or may have a lower portion angled with respect to side-directed light rays, as shown in U.S. Patent No. 4,143,394. While this approach may provide some increase in LED efficiency (where efficiency is measured by the proportion of the light emitted from a diode which is projected forward to a target) , the conventional casing shapes leave much room for improvement. Yet another approach is exemplified in U.S.

Patent No. 5,130,531. This approach involves forming a micro-Fresnel lens on the surface of a planar element and incorporating the planar element into the LED. The planar element may be supported within an LED casing adjacent to a diode. However, this configuration requires a complicated manufacturing process to assemble the lens-containing element in the casing. Alternatively, a stamper may be used to form a lens on a molded resin encapsulating the diode. However, this approach limits the shape of the LED that can be produced to a planar surface. Also, the '513 Patent refers to a "mold resin" which may be an epoxy resin. As all epoxy resins are of the thermosetting type, they are fluid enough to encapsulate a diode without damage to the wire bond, but they also harden into a molecular structure which cannot be remelted. Therefore, a micron-sized feature cannot be "stamped" into the surface of the molded resin with any degree of accuracy and repeatability.

Accordingly, there is a need for an improved LED having greater efficiency in terms of the amount of light emitted from a diode which is projected toward a target. There also is a need for a simple, inexpensive process for making such an LED.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, a light emitting device is provided which has a casing having a surface, at least one light emitting element, such as a diode, enclosed within the casing, and at least two wire leads, each wire lead having one end enclosed in the casing and electrically connected to the at least one light emitting element and an opposite end projecting from the casing. A molded diffractive optical element for focusing light emitted from the at least one light emitting element is formed on and integral with the surface of the casing.

According to another aspect of the present invention, a light emitting device is provided which includes a casing having a surface, at least one light emitting element, such as a diode, enclosed within the casing, and at least two wire leads, each wire lead having one end enclosed in the casing and electrically connected to the at least one light emitting element and an opposite end projecting from the casing. A plurality of v-shaped grooves are formed in the surface of the casing to reflect light emitted from the at least one light emitting element.

According to yet another aspect of the present invention, a light emitting device is formed by a method including the steps of providing a mold having a cavity, the cavity having a surface on which a diffractive optical element pattern is formed, positioning within the cavity at least one light emitting element for emitting light and at least two wire leads, each wire lead having one end electrically connected to the at least one light emitting element and a distal end, the at least one light emitting element being positioned so that the distal end of each wire lead protrudes from the cavity, and filling the cavity with an encapsulating material so that the material replicates an inverse of the diffractive optical element pattern.

These and other objects, features, and advantages of the present invention will be apparent from the following description, read in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a planar view of a conventional

LED.

Figures 2(a) and 2(b) are cross-sectional views of a conventional diode mold and a conventional LED formed using that mold.

Figure 3 is a cross-sectional view of a diode mold according to a preferred embodiment of the present invention.

Figure 4 is a planar view of an LED according to a preferred embodiment of the present invention having an optical element for focusing light formed on a curved portion of its surface.

Figure 5 is a cross-sectional view of a diode mold according to another preferred embodiment of the present invention. Figure 6 is a planar view of an LED according to another preferred embodiment of the present invention having v-shaped grooves formed in its surface. Figure 7 is a cross-sectional view of the LED shown in Figure 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

1. Introduction

According to the present invention, an LED is formed with an optically functional pattern molded in or on a particular portion of the casing surface. In this way, the functions of shaping and/or directing a light beam are incorporated into the molded LED structure to increase radiation efficiency without requiring a separate lens.

First, a method of forming the conventional LED 100 described above is explained with reference to Figures 2(a) and 2(b). A two-step process is used in which a diode mold is formed and then an LED is made using the mold. As shown in Figure 2(a), a diode mold 200 is formed having a diode cavity 210 with a cavity surface 220. The diode cavity 210 has the size and shape that are desired for the LED casing. As one example, the diameter of the cavity at the top may be 5-10 mm, the diameter of the cavity at the bottom may be 2-6 mm, and the length of the cavity from top to bottom may be 5-10 mm. The diode mold 200 is typically made of polypropylene and is durable enough to produce about 10-20 LEDs before it must be replaced. The diode mold 200 is usually prepared by injection-molding polypropylene resin into a steel mold used in an injection molding machine. The steel injection mold has an insert with a highly polished surface which is inserted at an appropriate area so that the cavity surface 220 is very smooth. LED 100 is then formed by positioning the diode 10 in the diode cavity 210 so that the wire leads 20 and 25 protrude from the diode cavity, and then filling the cavity with encapsulating resin. When the resin hardens, the LED is extracted by simply pulling it out of the mold, as shown in Figure 2(b). Since the cavity surface 220 was formed to be very smooth, the resulting LED has a clear, scratch-free surface.

2. First Embodiment

Next, a method of forming an LED according to the present invention is described with reference to

Figure 3. According to the present invention, a diode mold 300 has a diode cavity 310 having a cavity surface 320. A pattern corresponding to a desired optical element is formed in the cavity surface 320. In the first preferred embodiment, the pattern is that of a diffractive lens formed in the curved portion of the cavity surface 320 at the bottom of the cavity. Surface 320 features a diamond turned sample diffractive produced by using the following design formula:

Φ(r)=ar²+br⁴+... (1) Where: r=radial distance from the center of the LED a=-2.3xl0^ b=6.7xl0"⁷

In order to form diode mold 300, the polished steel injection mold insert conventionally used to form a smooth cavity surface is replaced with an insert having a predetermined pattern thereon. The pattern on the insert is preferably a micron-sized diffractive pattern formed by any of the following methods. If the pattern is radially symmetric with a period of greater than 1 micron, diamond-turning is the preferred method to produce a continuous surface, commonly known as a kinoform or blazed structure. If the pattern is radially symmetric with a period of less than 1 micron, then multi-layer photolithographic techniques such as ion-milling or reactive ion-etching are the preferred methods. These techniques will produce a multi-layer structure which closely approximates the continuous kinoform structure mentioned above. If the pattern is not symmetric at all, then the preferred method is multi-layer photolithographic techniques such as ion-milling or reactive ion-etching. Such patterns may be manufactured by the processes disclosed in U.S. Patent No. 5,538,674, incorporated herein by reference. Diode mold 300 is then formed by injection-molding polypropylene resin into a steel mold containing the patterned insert. The pattern is thus formed on the surface 320 of mold 300. Next, an LED is formed by accurately positioning a diode 410 and wire leads 420, 425 in the diode cavity 310 and filling the diode cavity 310 with an encapsulating resin, preferably an epoxy resin or other thermosetting resin. The encapsulating resin sets and replicates an inverse of the pattern on the mold surface 320. Generally, the process for forming the LED may be that utilized for any conventional method of manufacturing an LED from a mold. Typically, the diodes are made in strips of 5 to 15 units connected to a lead frame such that the entire frame, with attached dies, is lowered toward a series of mold cups, with each die located in one individual mold cup.

Figure 4 shows an LED 400 formed according to the first preferred embodiment of the present invention. The LED has a casing 430 formed by the hardened encapsulating resin. A molded diffractive optical element 450 is formed on and integral with a curved portion of the surface of casing 430. The diffractive optical element 450 is the inverse of the pattern formed in the cavity surface 320 and has corresponding features and dimensions. It functions as an embedded lens and shapes the light rays emitted from the diode 410 into a light beam 460 directed toward a target 470. Since the diffractive pattern 450 is closer to the light source than the separate lens 50 in the conventional arrangement of Figure 1, more light rays are collected and directed to the target. Yet, the LED 400 was formed by a simple process which does not require positioning a separate lens element.

The portion of the surface of casing 430 on which the optical element is formed is not limited to being curved. The optical element may likewise be formed on a flat surface, or any other continuous surface having a different geometry, by appropriate configuration of the diode cavity 310.

The pattern preferably comprises a diffractive optical element which may be either a holographic element (having a sinusoidal surface profile and prepared in the laboratory using photographic equipment typically associated with the preparation of holograms) or a non-holographic diffractive structure (a mathematically predetermined diffractive structure which is digitally designed, usually with a computer, and typically includes a number of non-sinusoidal linear surface features) . Non-holographic diffractive elements typically include blazed diffraction gratings, kinoforms, Damann gratings, and other diffractive microstructures including rectilinear surface features. Another non- holographic diffractive microstructure is a binary optical element which has a plurality of substantially only horizontal or vertical surface relief features.

These surface relief features can be employed in various patterns to achieve different effects such as dividing an incident light beam into a plurality of emergent light beams (e.g., a fanout grating), steering the light beam in a particular direction, passing light of only a particular wavelength (color filter) , correcting for refractive index changes which occur with changes in temperature, and correcting for changes in refractive index which occur with changes in the wavelength of the incident light (color correction) . Other optical functions which may be performed by the molded diffractive pattern include reducing penumbra, dispersion compensation, beam steering, optical multiplexing, light wave modulation, optical interconnecting a variety of signals, collimating, light wave redistributing, etc. These various optical functions may be achieved by designing the pattern, height, width, and periodicity of the diffractive surface features .

Depending upon the particular optical effect desired, the surface feature size will be some multiple of the grating height, where the multiple will determine the phase shift in units of wavelength. In practice, this multiple will generally be between 1/20 and 200 times the wavelength of the light. Typical values include 1/4, 1/2, 3/4, 1, 2, 3, etc. In general, for the plastic materials with visible light, this translates into feature heights on the order of micrometers.

The lateral dimensions or spacing of the features as well as the periodicity is determined differently for a diffractive patterns. Typically, the lateral dimensions were arranged from a fraction to a about a 1000 times the wavelength of light. For plastic materials with visible light, the range is generally between about 1/2 to about 100 microns.

The design of the diffractive can be achieved through mathematical modeling, using any of several techniques depending upon the level of sophistication required. These techniques include scalar analysis, rigorous coupled wave theory, parabasal ray tracing, vector analysis, and the beam propagation method. Commercially available codes can be employed to carry out the diffractive design analysis. Some of these codes include "Code V" or "Light Tools", both from Optical Research Associates (Pasadena, CA) , "ASAP" from Breault Research Organization (Tucson, AZ) , "Diffract" from MM Research (Tucson, AZ) , or "Grating Solver" from Grating Solver Development Corporation (Allen, TX) . Examples of this mathematical analysis are discussed in more depth in U.S. Patent No. 5,218,471 to Swanson et al., which is incorporated herein by reference.

The above-discussed mathematical techniques result in a mathematical model of the diffractive pattern. In the case of a rotationally symmetric diffractive, the mathematical description will take the form of the phase equation:

Φ(r)=Ar²+Br ⁴+Cr ⁶... (2) where Φ(r) is the phase of the diffractive structure as defined on the surface. This equation defines a rotationally symmetric diffractive structure where r is the radial distance on the lens from the vertex.

In the case of a repeating unit diffractive, the description will be a two-dimensional matrix of phase descriptors.

The physical description of the diffractive structure for a rotationally symmetric lens is defined by the Fresnel Zone Equation and the phase step height. The Fresnel Zone Equation defining the ring radii is: r_m=SQRT( (2mfλ/n+(mλ/n)²) (3) where r_m is the m-th f=focal length

by itself λ=free space design wavelength n=dielectric refractive index

A ring is located at each radius for which the phase is found to be an integer value. The phase step height as defined and stated above is determined by θ(r_m)=2τrm and is equal to λ/(n-l).

A more advanced application would be to closely balance the optical power of the refractive portion of the lens with the diffractive portion of the lens in such a way as to provide color correction, as mentioned earlier. This is possible because the optical power is linearly proportional to the wavelength. For a refractive surface, the optical power is a second order effect to the wavelength. In other words:

These values are generally solved iteratively with the aid of a computer.

The approach is similar for a repeating unit diffractive, but requires a greater number of computations because of the multiple cells. These approaches can be better understood with reference to the examples below.

By designing the diffractive mathematically, it is possible to achieve a high degree of control over the optical characteristics of the resultant lamp. The diffractive mask which results is a defined or pseudo- random phase mask, in contrast to a random phase masks achieved with HOE's recorded in a laboratory environment using optical components. In the defined phase mask, it is possible to determine with high precision the phase effect of the physical elements at each point on the mask before the lens itself is created. This permits the lens to be modeled in combination with the bulb and reflector, and the design to be tolerance-analyzed and optimized before a lens is ever actually fabricated. In addition, it is possible to customize the patterns with much more precision and flexibility than can be done with laser interferometry. Furthermore, it is possible to create diffractive structures which are not sinusoidal in profile.

Example 1 An LED was constructed in accordance with the first preferred embodiment as follows. A diode mold was formed by injection molding using an injection mold with an insert as described above. The insert had formed thereon a pattern corresponding to a diffractive lens as defined above in the equation (1) , which was designed to concentrate light into a plus or minus 30° cone with a uniform distribution within the cone. Therefore the surface of the diode cavity in the diode mold has a corresponding pattern. A standard TS aluminum gallium arsenide red diode with a wavelength of 670 nanometers diode having two wire leads was positioned in the diode cavity. The diode cavity was then filled with an encapsulating material. The material used was MG18 epoxy from Hysol. The material was cured at ambient conditions for 48 hours; however, the curing can be accelerated by heating the resin. The LED was removed from the mold and tested. A current of 20 milli-amps was applied to the wire leads, and it was observed that the light was concentrated within the desired plus and minus 30° cone, and the light had an average intensity which varied to plus or minus 20 percent.

3. Second Embodiment

A second preferred embodiment of the present invention is described next with reference to Figures 5-7. The LED according to this embodiment is referred to as an internally reflective inverted jellybean diode. As shown in Figure 5, a diode mold 500 is formed with a diode cavity 510 having a cavity surface 520. The cavity surface 520 has a series of V-shaped grooves formed therein (see Fig. 7) . The grooves are preferably arranged so that an apex of each lies in a plane that contains a central axis of the diode cavity, and so that they are symmetrical about the central axis. Holes 504 and 506 are formed at the bottom of the diode cavity 510. Below the cavity is a space 508 for receiving wire leads which protrude through the holes

504 and 506. The diode mold 500 can be formed using an injection-molding process with an appropriate insert to form the v-shaped grooves.

An LED is formed by placing a diode 610 and attached wire leads 620 and 625 at the bottom of the diode cavity 510 so that wire leads 620 and 625 project down through openings 504 and 506 into the space 508. Encapsulating resin is then added to the cavity. Because the encapsulating resin is chosen such that the viscosity is high enough to prevent leakage through the bottom holes, and because there is a close tolerance fit between the wire leads 620 and 625 and the openings 504 and 506, little or no encapsulant drains down through the openings to cover the wire leads.

Figure 6 shows an LED 600 formed using diode mold 500 and Figure 7 shows a cross-sectional view of LED 600 along the line VII-VII in Figure 6. LED 600 has a casing 630 formed by the hardened encapsulating resin. Casing 630 has an inverted jellybean diode shape with a flat end 645 and a plurality of v-shaped grooves 650 on its surface. Each of the grooves 650 has an apex that lies in a plane that contains a central axis of LED 600, and the grooves 650 are symmetrical about the central axis. The grooves 650 preferably have an angle θ in the range of 20° to 45° and serve as reflective surfaces which substantially reduce or prevent light emitted from diode 610 from exiting the side of casing 630 and which guide the light towards the flat end 645. As a light ray reaches the grooved surface of casing 630 it is reflected back toward the interior of LED 600 by the surface of a groove. The ray will reflect along a zig-zag path toward the flat end 645, as illustrated by light rays 640 in Figure 6. With this design, the grooves 650 provide a surface for substantially total internal reflection and essentially all the available light is captured and projected forward from the flat end 645 toward a target 670. The performance can be further enhanced by including an optical element, such as a diffractive lens described above, on the flat end 645. The diffractive lens can be formed immediately after the encapsulant is added to the cavity by placing a cap on the mold cup. The cap having a desired pattern for the diffractive molded into place on the inside surface thereof.

Example 2

An LED design was constructed in accordance with the second preferred embodiment as follows. The design had a pattern of v-shaped grooves, as shown in Fig. 7, having an angle of 65°. This design increased forward directed light by 50% above a reference design with a normal refractive lens.

4. Conclusion

Although two preferred embodiments have been described, those of ordinary skill will appreciate that numerous variations are possible. A diode mold need not be formed identically to diode mold 300 or diode mold 500, described above. For example, the mold cup could be formed in two halves with a vertical parting line. This eliminates the die-lock problem of the second embodiment and the need to load the LED leads through holes. Also, the pattern formed on the cavity surface to create an optical element on the LED casing surface need not be a diffractive pattern or a series of v-shaped grooves. It can be any other pattern desired to focus or direct light in a manner needed for a particular LED application. Further, although the patterns formed on the cavity surface in the preferred embodiments were formed by injection-molding in a diode mold using a shaped insert, the invention is not limited to that method. For example, the pattern on the cavity surface could also be formed by laser- cutting a pattern on the surface wall after the mold cup is formed. Also, the diode mold material is not limited to polypropylene. Other materials that can be molded to have an appropriate diode cavity and cavity surface pattern can also be used. Such materials would include, for example, injection-molded metal, or other injection, moldable resins, including examples such as, but not limited to, perfluoroalcoxy resin, acetal, nylon, polyethylene, or polycarbonate. Likewise, an LED need not comprise the identical components described in LED 400 or LED 600 above. For example, an LED according to the present invention is not limited to having a single diode. Multiple diodes may be embedded or enclosed in a single casing. In this case, each diode may have a corresponding pair of lead wires or multiple diodes may be connected to common lead wires, e.g., through a common conductive strip. Additionally, any other semiconductor emitter, such as a Vertical Cavity Surface Emitting Diode or Laser Diode, or a detector such as a photodetector, could be placed into a single casing in single or multiple pairs such that one emitter and one detector could form a reflective sensor module. Further, the encapsulating material need not be a thermosetting resin. It can be any material capable of enclosing a diode and forming an LED casing. The encapsulating material also need not be transparent, but may be colored if desired. Also, the shape of the LED casing is not limited to that of a jellybean diode or inverted jellybean diode. It is only necessary that the LED have a surface on which a pattern can be formed, and this can take the form of any continuous surface, such as a flat surface, a spherical surface, or an aspherical surface.

Since the diffractive surface according to the present invention is molded into the resin and not stamped therein, smaller and more accurate diffractive patterns can be produced. Stamping essentially remelts the resin and it may be in semi-liquid form when the stamper is removed from the resin, causing distortion in the pattern. Also, surface voids may be present in the stamped surface because of air pockets between the stamper and the resin, and because of minute amounts of resin which adhere to the stamper when it is removed. A molded pattern, on the other hand, is much more accurate and stable since the surface of the resin solidifies while in contact with the mold surface. Since the resin flows onto the mold surface as a liquid, air pockets are typically eliminated. Thus, the molded pattern is visually different from the stamped pattern in the accuracy, uniformity, and consistency of the surface relief features.

While the present invention has been described with reference to what are presently considered to be the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope of the claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims

WE CLAIM:

1. A light emitting device comprising: a casing having a surface; a light emitting element for emitting light enclosed within said casing; at least two wire leads, each wire lead having one end enclosed within said casing and electrically connected to said light emitting element and an opposite end projecting from said casing; and a molded diffractive optical element formed on and integral with the surface of said casing to diffract the light emitted from said light emitting element.

2. A light emitting device according to claim 1, wherein the casing surface includes a curved portion, and wherein at least a portion of the molded diffractive optical element is formed on said curved portion.

3. A light emitting device according to claim 1, wherein the diffractive optical element is one of a rotationally symmetric diffractive lens using a kinoform structure, a rotationally symmetric diffractive lens using a multi-layer structure, and a non-rotationally symmetric diffractive lens formed by etching a multi-layer structure.

4. A light emitting device according to claim 1, wherein the diffractive optical element is formed at a position on said casing opposite from where the ends of the wire leads project from said casing.

5. A light emitting device according to claim l, wherein said light emitting element comprises a plurality of diodes enclosed within said casing.

6. A light emitting device according to claim 1, wherein said light emitting device comprises two or more semiconductor devices capable of emitting or detecting light.

7. A light emitting device according to claim 1, wherein said casing is shaped like a jellybean diode.

8. A light emitting device according to claim 1, wherein said casing is formed of a thermosetting resin.

9. A light emitting device according to claim 8, wherein said molded diffractive optical element has micron-sized features.

10. A light emitting device comprising: a casing having a surface; a light emitting element for emitting light enclosed within said casing; at least two wire leads, each wire lead having one end enclosed within said casing and electrically connected to said light emitting element and an opposite end projecting from said casing, wherein a plurality of molded v-shaped grooves are formed in the surface of said casing to reflect light emitted from said light emitting element.

11. A light emitting device according to claim

10, wherein said casing has a central axis and an apex of each of the v-shaped grooves lies in a plane that contains the central axis.

12. A light emitting device according to claim 10, wherein said casing has a central axis and the v- shaped grooves are arranged symmetrically around the central axis.

13. A light emitting device according to claim 10, wherein the v-shaped grooves are formed with an angle in the range of 55┬░ to 75┬░.

14. A light emitting device according to claim 10, wherein said light emitting element comprises a plurality of diodes enclosed within said casing.

15. A light emitting device according to claim 10, wherein said light emitting device comprises two or more semiconductor devices capable of emitting or detecting light.

16. A light emitting device according to claim

10, wherein said casing is shaped like an inverted jellybean diode.

17. A light emitting device according to claim 10, wherein said casing has an exit surface which comprises one of a diffractive or refractive lens structure.

18. A light emitting device according to claim 10, wherein said casing is formed of a thermosetting resin.

19. A method of making a light emitting device, said method comprising the steps of: providing a mold having a cavity, the cavity having a surface on which a diffractive optical element pattern is formed; positioning within the cavity at least one light emitting element having two electrical leads, each lead having one end electrically connected to the light emitting element and a distal end, the light emitting element being positioned so that the distal end of each lead protrudes from the cavity; and filling the cavity with an encapsulating material so that the material replicates an inverse of the diffractive optical element pattern.

20. A method according to claim 19, wherein a portion of the surface of the cavity is curved and the pattern is formed on the curved portion of the surface.

21. A method according to Claim 19, wherein a portion of the surface of the cavity is flat and a pattern is formed on the flat surface.

22. A method according to claim 19, wherein said providing step comprises the steps of: providing an injection mold to form said mold having a cavity, there being an insert in the injection mold at a position corresponding to the cavity, an inverse of the diffractive optical element pattern being formed on the insert; and forming the mold having a cavity by an injection molding process using the injection mold and the insert.

23. A method according to claim 19, wherein the diffractive optical element pattern on the surface of o

the cavity is disposed on a curved portion of said surface.

24. A method according to claim 19, wherein the pattern on the surface of the cavity is a pattern of v- shaped grooves.

25. A method according to claim 24, wherein the cavity has a central axis and each of the v-shaped grooves lies in a plane that contains the central axis.

26. A method according to claim 24, wherein the cavity has a central axis and the v-shaped grooves are arranged symmetrically around the central axis.

27. A method according to claim 19, wherein the mold has a second cavity below said cavity having the pattern and has two holes connecting said cavity having the pattern to the second cavity, and wherein said positioning step comprises the step of positioning the light emitting element and the at least two wire leads so that the distal end of each wire lead passes through one of the two holes and projects into the second cavity.

28. A method according to claim 19, wherein said filling step comprises filling the cavity with a thermosetting resin.